1. Technical Field
The disclosed embodiments generally related to the field of electrostatic marking systems and corona charging components for these systems.
2. Description of the Related Art
In an electrostatographic process, a system is used hereby a uniform electrostatic charge is placed upon a reusable photoconductive surface. The charged photoconductive surface is then exposed to a light image of an original and the charge is selectively dissipated to form a latent electrostatic image of the original on the photoreceptor. The latent image is developed by depositing toner, finely divided marking and charged particles, upon the photoreceptor surface that become electrostatically attached to charged areas of the latent electrostatic image creating a visible replica of the original. The toned developed image is then transferred from the photoreceptor to a final image support material, such as, for example, paper, and fixed to the image support media by heat and pressure to form a permanent copy corresponding to the original.
In xerographic systems of this type, a photoreceptor surface may be arranged in a path through the various processing stations of the xerographic system. The photoconductive or photoreceptor surface may be reusable in that following transfer of the toner image to the support material several charging stations may be traversed that may expunge the photoreceptor surface of residual toner and prepare the photoreceptor to accept another latent electrostatic image for the reproduction of another original. For example, charging stations may be placed at positions where a uniform charge on the photoreceptor surface is necessary, such as, transfer stations, cleaning station, and the like.
A charging station may apply an electrostatic charge to a photoconductive or photoreceptor surface of a photoreceptor or photosensitive member using a number of methods such as, for example, electron-emitting pins, an electron-emitting grid, single corona-charging structures and single or multiple dicorotron wire assemblies. Corotrons, scorotrons, and dicorotrons, referred to herein collectively as “corotrons”, are commonly used in the xerographic process and use high voltage electricity to create the “corona” which is discharged onto the photoreceptor surface to place a uniform charge on the surface of the photoreceptor.
A “corona” may be defined as a localized collection, or “cloud”, of charged ions that may be influenced to move toward an oppositely charged target. Corotrons create a corona by placing a high direct current (DC) potential, which may be either positive or negatively charged, on a thin wire. In contrast, dicorotrons use an alternating current (AC) potential on a glass coated wire to create both positive and negative ions. The wire of a corotron makes up a corona-generating electrode that is typically highly conductive. The wire may be mounted in an elongated U-shaped housing between two insulating anchors called “insulators” which support and hold the wire in a singular plane within the housing. The corotron is, generally, located within close proximity to the photoreceptor surface, and a screen or shield with a DC bias, whose voltage may determine the polarity and amplitude of the charge placed on the photoreceptor, and may be used to direct the corotron's charge toward the photoreceptor.
A corona may contain any number of ions, for example, H+ and N4+ which are the major positive ions for both AC and positive DC devices, and negative ions such as, NOx− (nitrogen oxides where x=1 or 2). O3− (ozone), and the like are often found in negative DC discharge. AC devices (dicorotrons) may also produce ions including O−, OH−, O2−, NO2−, CO3−, and the like. Of these, ozone and nitrogen oxides may occur in relatively large amounts and may be emitted into the surrounding atmosphere during the charging process as an effluent. These compounds are, generally highly reactive with organic compounds, such as morpholine, and/or the photoreceptor itself producing lateral charge migration (LCM) and/or parking deletion which negatively affect the photoreceptor and the resulting copy. Currently, fans and/or special coatings are used to remove or neutralize the gasses to various degrees of success.
Nitric oxide deletions or parking deletions have been a pervasive and persistent problem in these electrostatic copying systems. The name arises from the idea that when charging devices are run for a long period of time a relatively large amount of nitrogen oxides (NOx) and ozone (O3) build up. These effluents become adsorbed on the surface of nearby solids, and when the machine is shut down, the photoreceptor stops rotation and becomes “parked” with a small area directly adjacent to the charge device. Over a short period of time, the adsorbed effluents are released from the charge device in a process known as outgassing. Since the photoreceptor is parked in very close proximity to the charge device, a small local area of the photoreceptor becomes damaged and may produce an area of missing image leading to the deletion nomenclature.
Lateral charge migration (LCM) may involve the deposit of conductive salts formed through the interaction of corona and atmospheric contaminants, such as morpholine and organic nitrates, on a photoreceptor. These deposits may create a film on the photoreceptor which causes blurring of the electrostatic image or an uneven distribution of toner on the surface of the photoreceptor and, in some cases, deletions of portions of the image.
Photoreceptors have also been shown to be sensitive to nitric acid-type compounds such as, for example, HNO3 and HNO2 that may be emitted during the electrostatographic process. HNO3 and HNO2 are a combination of the NOx produced by the charge device and water vapor that is naturally present in the air as humidity. Nitric acids attack certain molecules in the transport layer of the photoreceptor rendering them over conductive. This increased conductivity allows any developed charge on the photoreceptor to leak to ground in the area of the attack or spread in what is sometimes, mistakenly, referred to as lateral charge migration, and areas of the image near the acid attack appear blank or, to a lesser extent, blurry because toner is not developed to the photoreceptor in these areas.
The disclosure contained herein described attempts to address one or more of the problems described above.